As strategic resources, petroleum and natural gas have significant influences on economic security and stable development of a country. As the demand for petroleum and natural gas is increasing rapidly and the shallow oil and gas resources are depleted increasingly in China, the dependence of economic and industrial growth in China on foreign trade of petroleum is increased continuously. Facing the serious situation of energy resources, China is in urgent need for new superseding oil and gas resources. According to the result of the second run of national oil and gas resource assessment, the total quantity of oil resources is 94 billion tons, the total quantity of conventional gas resources is 38 trillion cubic meters, and the remaining oil and gas resources are mainly distributed in deep strata. Most deep reservoirs in China are deeper than 5,000 m, the deepest reservoirs are in depth of about 9,000 m presently, the downhole temperature is 180-260° C., and massive salt-gypsum formations exist in most regions. At present, ultra-deep well drilling is carried out in Daqing, South China Sea, Jilin, Xinjiang, Tarim, Dagang and other oilfields. Drilling fluids that are resistant to ultra-high temperature and high calcium (CaCl2≥1%) are the key to successful drilling in deep salt-gypsum formations. However, the existing drilling fluids can't meet the requirements for resistance to ultra-high temperature and reservoir protection under the condition of massive salt-gypsum formations. A series of severe technical difficulties incurred by drilling fluid failure at high temperatures, such as well wall collapsing, jamming of drilling tools, well blowout, and reservoir contamination, etc., are encountered in drilling engineering. In deep well drilling, drilling fluid failure at high temperatures may result in difficulties in cuttings carrying, suspension of weighting materials, and effective support of the well wall, and may cause severe safety accidents such as well caving, jamming of drilling tools, well blowout, etc., even lead to abandonment of the well. At present, in the use of water-based drilling fluids in drilling of ultra-high temperature wells that involve salt-gypsum formations, the performance of the drilling fluids is maintained mainly by increasing the dosage of treating chemicals. Such an approach not only involves high cost, heavy consumption of treating chemicals and frequent treatment, but also results in complex drilling accidents, severe reservoir contamination, low drilling rate, long drilling cycle, production safety and public safety risks, and has severe impacts on drilling quality, drilling rate and benefits, and even affects the attainment of geological objectives.
Therefore, it is of great practical significance to make research on plugging agents for temperature-resistant calcium-resistant water-based drilling fluids used in oil and gas reservoir protection and drilling fluids that have such properties.